This invention relates to a far ultraviolet-sensitive positive resist composition which can be used for micro-patterning in, e.g., semiconductor device fabrication. More particularly, it relates to a positive resist composition which is adapted to be exposed to far ultraviolet rays.
In recent years, ICs have ever been increasing the degree of integration. Fabrication of semiconductor devices for very large scale integration (VLSI), etc. now needs ultrafine patterning technology to achieve line widths of half micron or even smaller. To meet the demand, the wavelengths of aligners used for optical lithography have been getting shorter and shorter. Today, it is studied to use excimer laser (e.g., XeCl, KrF or ArF) light beams having shorter wavelengths in the far ultraviolet region.
A chemically amplified resist is used in lithographic patterning using such short wavelengths. While a chemically amplified resist is generally suited to be exposed to ultraviolet rays or far ultraviolet rays, it is required to satisfy requirements specific to the aligner used. Where KrF excimer laser light having a wavelength of 248 nm is used, for example, a resist composition containing a hydroxystyrene resin having an acetal or ketal group as a protective group has been proposed for its low light absorption. Although the composition is fit for exposure to KrF excimer laser light having a wavelength of 248 nm, it has low sensitivity to ArF excimer laser light having a wavelength of 193 nm on account of its essentially too large absorbance at 193 nm. The low sensitivity to ArF excimer laser light is accompanied with other disadvantages, such as reduced resolving power, reduced depth of focus (DOF) and deteriorated pattern profile. There remains much room for improvement in the composition proposed.
Resins having an alicyclic hydrocarbon moiety introduced thereto have been proposed for the purpose of imparting dry etching resistance to photoresist compositions for ArF laser light. The resins include those obtained by copolymerizing a monomer having a carboxylic acid (e.g., acrylic acid or methacrylic acid) moiety or a monomer having a hydroxyl group or a cyano group in the molecule with a monomer having an alicyclic hydrocarbon group.
JP-A-9-73173 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-10-161313 disclose a resist material containing an acid-responsive compound having an alkali-soluble group which is protected with an alicyclic group-containing structure and a structural unit which makes the alkali-soluble group be released by the action of an acid thereby to render the compound alkali-soluble.
JP-A-2000-137327 discloses a resist composition containing a resin having an adamantyl-containing repeating unit in an attempt to improve sensitivity, resolution, and adhesion to a substrate.
JP-A-2001-183836 proposes a resist composition exhibiting satisfactory resist performance and improved wettability by an alkali developing solution, which contains a resin comprising a repeating unit carrying an acid-labile group having an adamantyl group and a repeating unit carrying an adamantyl group substituted with two hydroxyl groups.
JP-A-2001-109154 teaches a resist composition containing a resin having a repeating unit having an alicyclic lactone structure in an attempt to improve sensitivity, resolution, and line edge roughness.
However, none of these related arts succeeds in sufficiently improving line edge roughness. xe2x80x9cLine edge roughness (LER)xe2x80x9d means irregularities of edges of lines patterned in the resist as observed in the direction perpendicular to the lines. When seen right from above, a line pattern shows a roughness of plus or minus several tens of nanometers with respect to a reference line. Since LER is transferred to the substrate on etching, large LER leads to deterioration of electrical characteristics, resulting in a reduced yield. Reduction of a resist pattern size below a quarter micron has being boosting the demand to reduce LER.
An object of the present invention is to provide a positive resist composition which provides a resist pattern with markedly reduced LER and is suitable to a supermicro-lithographic process and other photofabrication processes in the fabrication of VLSIs, high capacity microchips, etc.
The present inventors have conducted extensive studies on materials of a chemically amplified positive resist composition and found as a result that the object of the invention is accomplished by:
(1) A positive resist composition comprising (A) a resin which contains a repeating unit represented by formula (I): 
wherein R1 represents a hydrogen atom or an alkyl group; A1 represents a single bond or a linking group; R2 represents an alkylene group; and X represents an alkoxy group or a hydroxyl group,
and exhibits an increased rate of dissolution in an alkali developing solution by the action of an acid and (B) a compound capable of generating an acid on exposure to active light rays or a radiation.
(2) The positive resist composition according to (1), wherein the resin (A) comprises a repeating unit represented by formula (II): 
wherein R represents a hydrogen atom or a methyl group; A2 represents a single bond or a linking group; and ALG represents an alicyclic hydrocarbon group-containing group represented by formula (pI), (pII), (pIII), (pIV) or (pV): 
wherein R11 represents a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or a sec-butyl group; Z represents an atomic group necessary to form an alicyclic hydrocarbon group together with the adjacent carbon atom; R12, R13, R14, R15, and R16 each represent a straight-chain or branched alkyl group having 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R12, R13, and R14 and at least one of R15 and R16 represent an alicyclic hydrocarbon group; R17, R18, R19, R20, and R21 each represent a hydrogen atom, a straight-chain or branched alkyl group having 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R17, R18, R19, R20, and R21 represents an alicyclic hydrocarbon group and that at least one of R19 and R21 represents a straight-chain or branched alkyl group having 1 to 4 carbon atoms or an alicyclic hydrocarbon group; and R22, R23, R24, and R25 each represent a straight-chain or branched alkyl group having 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R22, R23, R24, and R25 represents an alicyclic hydrocarbon group; and R23 and R24 may be connected together to form a ring.
(3) The positive resist composition according to (1) or (2), wherein the resin (A) further comprises a repeating unit represented by formula (III): 
wherein R3 represents a hydrogen atom or a methyl group; A3 represents a single bond or a divalent linking group; Z3 represents an alicyclic hydrocarbon group having a valence of (p+1); and p represents an integer of 1 to 3.
(4) The positive resist composition according to (1), (2) or (3), wherein the resin (A) further comprises a repeating unit having a cyclohexane lactone moiety, a norbornane lactone moiety or an adamantane lactone moiety.
(5) The positive resist composition according to (3), wherein the repeating unit represented by formula (III) is a repeating unit represented by formula (IIIa): 
wherein R30 represents a hydrogen atom or a methyl group; and R31, R32, and R33 each represent a hydrogen atom, a hydroxyl group or an alkyl group, provided that at least one of R31, R32, and R33 is a hydroxyl group.
(6) The positive resist composition according to (5), wherein at least two of R31, R32, and R33 each represent a hydroxyl group.
(7) The positive resist composition according to (2), wherein, in formula (II), A2 is a single bond, and ALG is a group represented by formula: 
wherein R26 and R27 each represent a straight-chain or branched alkyl group having 1 to 4 carbon atoms.
(8) The positive resist composition according to any one of (1) to (7), wherein the resins (A) further comprises a repeating unit having a lactone moiety and represented by formula (IV) 
wherein R1a represents a hydrogen atom or a methyl group; W1 represents a single bond or one of, or a combination of two or more of, an alkylene group, an ether group, a thioether group, a carbonyl group, and an ester group; Lc represents a lactone structure of formula: 
wherein Ra1, Rb1, Rc1, Rd1, and Re1 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and m and n each represent an integer of 0 to 3, provided that m+n is 2 to 6.